Method and apparatus for optimizing output power levels in power amplifiers

ABSTRACT

Some embodiments discussed relate to an apparatus comprising a power amplifier module. The power amplifier module includes a plurality of sensors, and a first digital communication port configured to provide a monitor signal from at least one of the plurality of sensors. The apparatus includes a transceiver module coupled to provide an signal to an input of the power amplifier the transceiver module including a second digital communication port configured to receive the monitor signal from the first digital communication port, a processing unit configured to generate at least one of a bias control signal and a back-off signal dependent upon the monitor signal, and a power controller to receive the at least one of bias control signal and the back-off signal and provide at least one further input signal to the power amplifier based on at least one of the bias control signal and the back-off signal.

RELATED APPLICATIONS

This patent application claims the benefit of priority, under 35 U.S.C.Section 119(e), to U.S. Provisional Patent Application Ser. No.60/863,483, filed on Oct. 30, 2006, which is incorporated herein byreference.

TECHNICAL FIELD

Embodiments described herein relate generally to power amplifiers andmore particularly, to optimizing the output power levels in poweramplifiers.

BACKGROUND

Global System for Mobile Communications (GSM) is one of the standardsused for mobile phones. Gaussian Minimum Shift Keying (GMSK) is a typeof continuous-phase frequency-shift keying used in GSM. Enhanced Datarates for GSM Evolution (EDGE) is a digital mobile technology used inconjunction with GSM to provide packet-switched applications such asinternet connection. EDGE additionally uses 8 phase-shift keying (8PSK)as part of the modulation and coding scheme.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of an apparatus for optimizing theoutput power levels of power amplifiers, according to some embodimentsof the invention.

FIG. 2 illustrates a table showing various power control parameterstored for each transmission channel, according to some embodiments ofthe invention.

FIG. 3 shows a method for optimizing the output power levels of poweramplifiers, according to some embodiments of the invention.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and structural, logical,and electrical changes may be made without departing from the scope ofthe invention. The various embodiments are not necessarily mutuallyexclusive, as some embodiments can be combined with one or more otherembodiments to form new embodiments.

The growth and use of radio-frequency devices (such as hand-helddevices) with increasing functional capabilities (e.g., voice, video,and data) has resulted in a greater demand for efficient power-savingtechniques to increase the battery life in these devices.Energy-efficient linear power amplifiers are essential components inmobile battery operated systems having wireless connectivity, e.gcellular phones, personal digital assistants (PDAs).

Linearity in power amplifiers is a fundamental requirement for theoperation of 8PSK based modulation schemes in mobile handsets. Anyamplitude distortion of the signal envelope produces two unacceptablephenomena. Firstly, the spectrum of the signal is widened (also known asspectral re-growth). This widening effect can cause the signal to failthe prescribed modulation mask, a requirement set by the GSM standardsto prevent interference to neighboring channels. Secondly, a simpledistortion of the modulation constellation results in a lowered signalto noise ratio at the receiver. The GSM standards define an error vectormagnitude (EVM) specification, which is a measure of the differencebetween the transmitted signal and an ideal one. In practice,imperfections in the modulator, other transmitter stages andnon-linearity in the power amplifier can consume a significant fractionof the EVM budget.

In applications like the EDGE standard, a modified 8PSK modulationscheme is used where as a result of base-band filtering, the finalmodulation signal is also amplitude modulated which means a non-constantenvelope is present. Consequently, due to the presence of a non-constantenvelope, the spectrum at the output of power amplifier strongly dependson the linearity of the power amplifier used. Hence, it is desired tohave power amplifiers used in applications having 8PSK modulationschemes to be optimized in order to meet the stringent linearityrequirements. Moreover, it is desired to limit the maximum poweramplifier current in applications using GMSK as the modulation scheme.Furthermore, it is also desired to prevent power amplifiers frombreakdown due to excessive heat.

In some embodiments, since mobile devices using EDGE technology supporttwo types of modulation schemes, the power amplifiers are also requiredto support two different working modes in such devices.

In a GMSK modulation scheme, the modulation is of constant envelopetype. Here, the linearity of the power amplifier does not corrupt themodulation quality and it is therefore not an issue (as long as theharmonics stay below a certain threshold). However, the requirement onmaximum power is important, because of the presence of (1) high peakcurrents and (2) greater heat generation within the power amplifier.Most handset manufacturers desire to have the maximum current drawn bythe power amplifier to be limited. This would enable in maximizing thetalk time and avoiding abrupt self switching-off of the mobile due tothe drop in battery voltage.

On the other hand, in 8PSK the linearity plays a big role, since a nonlinear power amplifier generates unwanted side-lobes next to the activechannel which can violate the European Telecommunications StandardInstitute (ETSI) requirement on spectrum purity. It is thereforeimportant to back-off the transmitting power when the power amplifier isoperating in a region where the nonlinearity is too strong.

However, both maximum current (consequently, the heat generation) andlinearity strongly depend upon the actual working conditions andparameters of the power amplifier, especially the parameters such asinstantaneous load, temperature and supply voltage. In order to optimizethe system performance, it is desirable to make the back-off dependenton actual load condition, so that an unnecessarily large back-off isavoided. Additionally, having a large back-off may lead to using biggerpower amplifiers with lower efficiency.

In some embodiments, since the load condition depends heavily on theactual frequency, a system and method to pair the back-off or biasingconditions with the frequency is used. In some embodiments, such asystem that pairs the back-off with the frequency is particularly usefulwhen the mobile system is operating in frequency-hopping mode in whichcase the channel is continuously changed. In some embodiments, thesystem works on slot basis where the system detects the state of thepower amplifier after a burst and takes appropriate action for the nextset of bursts. By implementing this system, an improved power amplifierworking condition along with a better switching spectrum is achieved.

In some embodiments the power amplifier has a power detector. In someembodiments, power amplifier has sensors including internal currentsensors, temperature sensors, and linearity sensors. In someembodiments, a digital information from sensors is sent from the poweramplifier to the transceiver using a digital communication link betweendigital communication ports located within the transceiver and poweramplifier, respectively.

In some embodiments, after the transmission of either a GMSK or 8PSKslot, the transceiver activates the digital link to the power amplifierin order to monitor its status. In some embodiments, the status reportindicates the temperature at power amplifier and whether a maximumcurrent threshold has been overtaken (e.g., in the case of GMSK) orwhether the linearity of power amplifier was not good enough (e.g., inthe case of 8PSK). In some embodiments, the status report may alsoinclude the amount of battery power remaining. In some embodiments,information regarding the amount of remaining battery power is evaluateddirectly at the transceiver.

In some embodiments, one of two modes are available (i) either to set amaximum current or (ii) to provide linearity. In some embodiments, forsubsequent transmission operations on a particular channel, the maximumpower is limited (e.g., in the case GMSK) or the bias condition of thepower amplifier is changed (e.g., in the case of 8PSK).

In some embodiments, it may also be necessary to back off the power ifthe temperature of the power amplifier is too high (to avoid burn up ofthe device) or if the battery voltage is below a certain threshold (thiscould happen regardless of the particular frequency being used).

FIG. 1 is a schematic view of apparatus 100 for optimizing the outputpower level of power amplifiers, according to some embodiments of theinvention. Apparatus 100 includes an RF transceiver module 102, and apower amplifier module 130. Power amplifier module 130 is electricallycoupled to an antenna 142 using a link 140. RF transceiver 102 includesa processing circuit 104, a power controller 110, a summing circuit 115and a digital port interface 120. Processing circuit 104 includes aprocessor 106 and a memory 108. Power amplifier 130 includes a digitalport interface 132, a temperature sensor 134, an internal current sensor135, a linearity sensor 136, and a power detector 137. Digital portinterface 120 of RF transceiver 102 and the digital port interface 132of power amplifier 130 are coupled using a digital communication link122.

Sensor information related to conditions experienced by power amplifiermodule 130 as measured by 134, 135, 136, and 137 is communicated frompower amplifier 130 to RF transceiver 102 using digital port interfaces120, 132 and digital communication link 122. In some embodiments,digital port interface 120 is a serial port interface (SPI).

Summing circuit 115 receives an initial signal on line 114 generated ata baseband circuit module (not shown) and a back-off signal on line 116generated at processing circuit 104. Summing circuit 115 combines thesignals on lines 114 and 116 and sends the combined signal to powercontroller 110, which in turn provides an input signal on line 126 topower amplifier module 130. Input signal on line 126 is received at aninput terminal of power amplifier 130. Additionally, processing circuit104 generates a bias control signal on line 118 based on power amplifieroperating information received at processing circuit 104 from sensors134, 135, 136, and 137. A bias control signal provided on line 118 isreceived at power controller 110. Based on the bias control signal online 118, power controller 110 communicates to power amplifier 130 aV_(RAMP/Bias) voltage signal on line 124. Additionally, power amplifier130 provides a feedback signal V_(DET) on line 128 back to powercontroller 110. In some embodiments the V_(DET) signal is a feedbacksignal and V_(RAMP/Bias) changes the gain of RF power amplifier 130.

FIG. 2 illustrates a table 200 showing various power control parametersstored for each transmission channel, according to some embodiments ofthe invention. Row 202 shows the temperature of power amplifier 130sensed by temperature sensor 134. Row 204 lists channels used forfrequency-hopping. Row 206 corresponds to the back-off voltages to beapplied to the initial signal on line 114 for each corresponding channellisted in row 204. Row 208 lists the bias voltages of bias controlsignal in line 118 for each corresponding channel listed in row 204. Insome embodiments, the output power of power amplifier 130 is controlledbased on the values of bias voltages and back-off voltages.

In some embodiments, the RF transceiver 102 maintains a table 200 (shownin FIG. 2) with the necessary back-off and biasing conditions determinedfor each of the channels used for transmission. In some embodiments, thedimension of this table (maximum number of channels) depends on themaximum number of the different frequencies used in a frequency hoppingscenario. In some embodiments, the back-off can be gradually increasedor reduced over many bursts (with or without hysteretic behavior)according to whether the sensors measuring the linearity, theover-current, or the over-temperature remain active or not.

In some embodiments, the transceiver optimizes the power amplifieroutput power and/or the power amplifier biasing conditions according todigital information gathered through a digital link between poweramplifier and transceiver. In some embodiments (e.g., in the case ofGMSK), the output power of the power amplifier is reduced depending onthe status of the current sensor, or if the maximum temperature isexceeded. In some embodiments (e.g., in the case of 8PSK), the biasvoltage to the power amplifier is changed upon sensing an increase inquiescent current and the linearity sensor reports bad linearity. Insome embodiments, a table is used to store the necessary back off andbiasing condition for different channels. Storing the back-off andbiasing conditions improves system performances in a frequency-hoppingscenario. In some embodiments, the back off or biasing increase isperformed only on those channels where it is really necessary.

FIG. 3 shows a method 300 for optimizing the output power levels ofpower amplifiers, according to some embodiments of the invention.

At block 302, the apparatus is generating a monitor signal at a sensorin a power amplifier. At block 304, the action is sending the monitorsignal using a digital communication port to a transceiver. At block306, the action is receiving the monitor signal at a transceiver using adigital communication port. At block 308, the action is processing themonitor signal to generate a bias control signal and a back-off signal.At block 310, the action is receiving the bias control signal and theback-off signal at a power controller. The power controller isgenerating a power amplifier input signal based on an initial signal,the back-off signal, and the bias control signal.

The system for controlling output power disclosed in this invention issuitable for applications in various wireless data and voicecommunications standard and protocols, including GSM, General PacketRadio Service (GPRS), Code Division Multiple Access (CDMA), IEEE 802.11and others. In addition, the system discussed may be used in a widerange of wireless communication devices such as cellular phone, mobilecomputers, and other handheld wireless digital devices.

The accompanying drawings that form a part hereof show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.

Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description. In the previous discussion andin the claims, the terms “including” and “comprising” are used in anopen-ended fashion, and thus should be interpreted to mean “including,but not limited to . . . ”.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment.

1. An apparatus comprising: a power amplifier module including: aplurality of sensors, and a first digital communication port configuredto provide a monitor signal from at least one of the plurality ofsensors; and a transceiver module coupled to provide an signal to aninput of the power amplifier the transceiver module including; a seconddigital communication port configured to receive the monitor signal fromthe first digital communication port, a processing unit configured togenerate at least one of a bias control signal and a back-off signaldependent upon the monitor signal, and a power controller to receive theat least one of bias control signal and the back-off signal and provideat least one further input signal to the power amplifier based on atleast one of the bias control signal and the back-off signal.
 2. Theapparatus of claim 1, wherein the plurality of sensors includes at leastone of a temperature sensor, an internal current sensor, a linearitysensor, and a power sensor.
 3. The apparatus of claim 1, wherein theprocessing unit further comprises a memory to store a table including aplurality of back-off signals and a plurality of biasing signals.
 4. Theapparatus of claim 3, wherein each of the plurality of back-off signalsand the plurality of biasing signals corresponds to differentcommunication channels.
 5. The apparatus of claim 1, further comprisingan antenna adapted to send and receive signals from the transceivermodule.
 6. The apparatus of claim 1, further comprising a summingcircuit configured to combine the back-off signal and the input signaland provide the combined signal to the power controller.
 7. Theapparatus of claim 1, wherein the power controller is configured toreceive a feedback signal from the power amplifier.
 8. A methodcomprising: generating a monitor signal from at least one of a pluralityof sensors in a power amplifier; sending the monitor signal using afirst digital communication port in the power amplifier; receiving themonitor signal at a transceiver using a second digital communicationport; processing the monitor signal and generating a bias control signaland a back-off signal; and receiving the bias control signal and theback-off signal at a power controller and generating a power amplifierinput signal based on an initial signal, the back-off signal and thebias control signal, wherein the power amplifier input signal isreceived at the power amplifier.
 9. The method of claim 8, furthercomprising storing the bias control signal and the back-off signalcorresponding to a particular frequency channel in a memory.
 10. Themethod of claim 9, further comprising using the stored bias controlsignal and the back-off signal corresponding to the particular frequencyfor subsequent burst of transmission in a frequency-hop application. 11.The method of claim 8, wherein storing the bias control signal and theback-off signal includes storing the bias control signal and theback-off signal for different communication channels in a table within amemory.
 12. The method of claim 8, wherein generating a monitor signalfrom the plurality of sensors includes generating a monitor signal fromat least one of a temperature sensor, an internal current sensor, alinearity sensor, and a power sensor.
 13. The method of claim 8, furthercomprising combining the back-off signal and the initial signal andproviding the combined signal to the power controller.
 14. The method ofclaim 8, further comprising receiving a feedback signal from the poweramplifier at the power controller.
 15. A system comprising: a poweramplifier module including: a plurality of sensors, and a first digitalcommunication port configured to provide a monitor signal from at leastone of the plurality of sensors; a transceiver module coupled to providean signal to an input of the power amplifier the transceiver moduleincluding; a means for receiving the monitor signal from the firstdigital communication port, a means for generating at least one of abias control signal and a back-off signal based on the monitor signal,and a means for receiving the at least one of bias control signal andthe back-off signal and provide at least one further input signal to thepower amplifier based on at least one of the bias control signal and theback-off signal; and an antenna adapted to send and receive signals fromthe transceiver module.
 16. The system of claim 15, wherein theplurality of sensors includes at least one of a temperature sensor, aninternal current sensor, a linearity sensor, and a power sensor.
 17. Thesystem of claim 15, wherein the processing unit further comprises amemory to store a table including a plurality of back-off signals and aplurality of biasing signals.
 18. The system of claim 17, wherein eachof the plurality of back-off signals and the plurality of biasingsignals corresponds to different communication channels.
 19. The systemof claim 15, further comprising an antenna adapted to send and receivesignals from the transceiver module.
 20. The apparatus of claim 15,further comprising a summing circuit configured to combine the back-offsignal and the input signal and provide the combined signal to the powercontroller.